Typically, plasma display panels (“PDP”s) are display devices in which ultraviolet light excites phosphors in vacuum, thereby creating gas discharge in discharge cells. PDPs are the next generation thin-film display devices and can be manufactured with large high-resolution screens.
PDPs display letters or graphics using the light emitted from the plasma generated upon discharging the gas. That is, plasma is discharged to generate ultraviolet light upon application of voltage to two electrodes mounted within the discharge space of the plasma display panel. The ultraviolet light then excites the patterned phosphor layers to display a certain image.
Plasma display panels are generally classified into three types: an alternating current type (AC type), a direct current type (DC type) and a Hybrid type. FIG. 4 is a partial perspective view of a discharge cell of a conventional alternating current plasma display panel. As shown in FIG. 4, a conventional plasma display panel 100 comprises a first substrate 111, a plurality of address electrodes 115 formed on the first substrate 111, a dielectric layer 119 formed on the first substrate 111 over the address electrodes 115, a plurality of barrier ribs 123 formed on the dielectric layer 119 to maintain discharge distance and to prevent cross talk between cells, and phosphor layers 125 formed on the surface of the barrier ribs 123.
A plurality of discharge sustain electrodes 117 are formed on the second substrate 113, are positioned facing the first substrate 111, and are spaced apart from the address electrodes 115 on the first substrate 111. A dielectric layer 121 is positioned on the discharge sustain electrodes 117, and a protection layer 127 is positioned on the dielectric layer 127. The protection layer 127 mainly comprises MgO because MgO is transparent enough to transmit visible rays, effectively protects the dielectric layer and emits secondary electrons. Recently, it has been suggested to include additional materials in the protection layer.
The MgO protection layer is a transparent thin film having a sputtering-resistant characteristic. The protection layer absorbs the ion collisions produced by the discharge gas upon discharge during driving of the plasma display panel, thereby protecting the dielectric layer from the ion collisions and decreasing the discharge voltage by emitting secondary electrons. The protection layer is generally formed on the dielectric layer and generally ranges in thickness from 5000 Å to 9000 Å. The MgO protection layer may be formed by sputtering, electron beam deposition, ion beam assisted deposition (IBAD), chemical vapor deposition (CVD), sol-gel techniques and so on. Recently, ion plating has been developed and used to form a MgO protective layer.
Electron beam deposition provides a MgO protection layer by accelerating an electron beam with electric and magnetic fields and colliding that electron beam with the MgO deposition material. The deposition material is then heated and evaporated. Sputtering provides a denser protection layer with improved crystal alignment, but involves increased production costs. In sol-gel methods, the MgO protection layer is formed as a liquid.
Ion plating has recently been suggested as an alternative to form a variety of MgO protection layers. In this method, the evaporated particles are ionized and form a target. Ion plating has characteristics similar to those of sputtering, namely adhesion and crystallinity of the MgO protection layer, but can be carried out at high speeds, for example 8 nm/s.
Because the MgO protection layer contacts the discharge gas, discharge characteristics largely depend on the composition and characteristics of the protection layer. The characteristics of the MgO protection layer depend on the composition of the layer and the condition of the layer when formed. Therefore, a need exists for a MgO protective layer having a composition which improves the characteristics of the layer.
The protection layer mainly comprises MgO, and can be either a single crystal type or a sinter type. The sinter type protection layer has a faster response time than the single crystal material, but the response time is dependent on temperature and therefore changes with the environmental temperature. This temperature dependence substantially decreases discharge reliability and driving stability, and is therefore not suitable for mass production.
The single crystal protection layer has low temperature dependence, but slow response time, making it difficult to respond to the driving of a single scan and to produce a high definition PDP. These characteristics are confirmed by address discharge delay measurements taken at specific temperatures for PDP protection layers prepared by heat deposition of both a single crystal MgO material and a sinter material.